The present disclosure relates generally to near-eye-display (NED) systems, and more specifically to light field expansions that increase a size of an exit pupil of the NED.
Near-eye light field displays project images directly into a user's eye. Conventional NEDs generally include a small input beam that generates a source light field that is ultimately conveyed to a user's eye. The exit pupil of the NED is the virtual aperture of the NED surface through which the light field can be out-coupled to the user's eye. NEDs used in artificial reality systems (e.g. virtual reality (VR), augmented reality (AR), mixed reality (MR) systems or some combination and/or derivatives thereof) ideally have a large exit pupil. A large exit pupil allows users with variable interpupillary distance (IPD) to view images displayed in the NED without requiring a custom build of the NED hardware for each user. Additionally, the larger exit pupil accommodates eye rotation as a user views virtual objects in an artificial reality environment displayed by the NED. Because the input beam is typically much smaller than a desired exit pupil size, the input beam is expanded within the NED before being out-coupled to the user's eye.
Conventional techniques of exit pupil expansion (EPE) involve replicating the input beam and out-coupling the replications across the desired exit pupil. However, these conventional EPE solutions often lack luminance uniformity, since it is difficult to precisely out-couple the same flux of light across the entire eye box, as well as suffer from power inefficiency, since coupling efficiency is often sacrificed to provide uniform flux across the exit pupil. A main limitation is that conventional EPE solutions are static design solutions, resulting in specific, hardwired configurations of couplers and expansions within the NED that are not able to dynamically respond to a user, thus limiting the design and capabilities of the NED.